progress: support ReadCloser

Signed-off-by: Sumner Evans <sumner.evans@automattic.com>

Author: sumnerevans

progress/reader.go

@@ -2,9 +2,9 @@ package progress
 
 import "io"
 
-// Reader is an [io.Reader] that reports the number of bytes read from it via a
-// callback. The callback is called at most every "updateInterval" bytes. The
-// updateInterval can be set using the [Reader.WithUpdateInterval] method.
+// Reader is an [io.ReadCloser] that reports the number of bytes read from it
+// via a callback. The callback is called at most every "updateInterval" bytes.
+// The updateInterval can be set using the [Reader.WithUpdateInterval] method.
 //
 // The following is an example of how to use [Reader] to report the progress of
 // reading from a file:
@@ -44,4 +44,11 @@ func (r *Reader) Read(p []byte) (n int, err error) {
 	return n, nil
 }
 
-var _ io.Reader = (*Reader)(nil)
+func (r *Reader) Close() error {
+	if closer, ok := r.inner.(io.Closer); ok {
+		return closer.Close()
+	}
+	return nil
+}
+
+var _ io.ReadCloser = (*Reader)(nil)

progress/reader_test.go

@@ -2,6 +2,7 @@ package progress_test
 
 import (
 	"bytes"
+	"errors"
 	"io"
 	"testing"
 
@@ -24,3 +25,35 @@ func TestReader(t *testing.T) {
 	assert.Greater(t, len(progressUpdates), 1)
 	assert.IsIncreasing(t, progressUpdates)
 }
+
+type testReader struct {
+	*bytes.Reader
+	closed bool
+}
+
+func (r *testReader) Close() error {
+	if r.closed {
+		return errors.New("already closed")
+	}
+	r.closed = true
+	return nil
+}
+
+func TestReadCloser(t *testing.T) {
+	readCloser := &testReader{Reader: bytes.NewReader(bytes.Repeat([]byte{42}, 1024*1024))}
+
+	var progressUpdates []int
+	progressReader := progress.NewReader(readCloser, func(readBytes int) {
+		progressUpdates = append(progressUpdates, readBytes)
+	})
+
+	data, err := io.ReadAll(progressReader)
+	assert.NoError(t, err)
+	assert.Equal(t, data, bytes.Repeat([]byte{42}, 1024*1024))
+
+	assert.Greater(t, len(progressUpdates), 1)
+	assert.IsIncreasing(t, progressUpdates)
+
+	assert.NoError(t, progressReader.Close())
+	assert.ErrorContains(t, progressReader.Close(), "already closed")
+}